Enhancing the 3-dB Bandwidth via the Gain-Lever Effect in Quantum-Dot Lasers

Modulation response of a long-cavity, gain-levered quantum-dot semiconductor laser

“…The least responsive (lowest modulation efficiency) case was observed under uniform bias conditions; this case describes all 16 sections of the device being biased at the same current density, 500 A/cm 2 , while only one section was RF modulated. This modulation efficiency improvement result agrees with theoretical predictions, given the saturated gain at this bias condition [2,7]. For each case where the bias in the modulation section was reduced, the gain section's bias current was increased to maintain a constant output power.…”

“…On the other hand, if the entire device is modulated, the standard two-pole response is found and a less-than-optimal differential gain is realized limiting the modulation efficiency of the device. It also implies that the approximations used in deriving the analytic modulation response of a gain-levered laser do not hold for this long-cavity, multi-section quantum-dot device [2,13]. A corresponding response is given in Fig.…”

“…As a consequence of the relationship between differential gain and carrier density, cavity photons may be more efficiently modulated in a section subject to a lower biasing current [1]. While improving the modulation efficiency, the gain-lever effect is also observed to enhance the 3-dB modulation bandwidth [2]; such improvements achieved through the alteration of a laser's electrical biasing conditions are highly attractive, given that various other means of improving a laser's modulation characteristics involve external light sources (optical injection-locking) [3,4] or external feedback control mechanisms [5,6].…”

“…While previous studies of the gain-lever effect in quantum-dot lasers have utilized 4:1 gainto-modulation section ratios in short-cavity lasers (< 1 mm) [2], this work investigates an extreme gain-lever case, where the gain-to-modulation section ratio is 15:1 in a long-cavity laser (> 8 mm). These unique experimental results of representative extreme asymmetric bias cases (15:1 and 14:2) highlight the limit to the gain-to-modulation section ratio discussed numerically in [2] and compared with the single-section modulation response (0:16).…”

Enhanced Modulation and Noise Characteristics in 1.55 µm QD Lasers using Additional Optical Pumping

“…A research report has also revealed that via band structure engineering, the dynamic characteristics of QD lasers can be tailored [14]. Several structural and technical solutions such as using tunneling injection [15], pdoping [16], two sections gain lever [17], injection locking [18], or operating at excited state emission [19] have been suggested to overcome the mentioned restrictions on the modulation bandwidth of QD lasers. One of technical suggestions for improving the modulation response of QD laser is optical locking.…”